KLEEFSTRA R, VAN DIJK A-J, NIENHUIS J, SCHEKKERMAN H & VAN TURNHOUT C (2021) Breeding Eurasian Curlews Numenius arquata in the Netherlands: distribution, trends and breeding success of a wader in trouble. LIMOSA 94 (1): 4-18.

Throughout Europe numbers of breeding Eurasian Curlew seriously declined over the last decades and the species is classified as globally Near Threatened on the IUCN Red List of Threatened Species. The Dutch breeding population shows a similar negative trend and the Eurasian Curlew disappeared as a breeding bird in a lot of habitats in the last decades. This was reason for Vogelbescherming Nederland (BirdLife the Netherlands) and Sovon Vogelonderzoek Nederland (Dutch Centre for Field Ornithology) to declare 2019 the year of the curlew, in which data from monitoring projects and historical sources were analysed to detect which factors influence the numbers and distribution of breeding Eurasian Curlews and how they developed over time.
The long-term trend of breeding Eurasian Curlew in the Netherlands was positive until the late 1970s, but declined since (Fig. 1). Over the whole period (1975-2019) the decline was 1.9% per year, but in the last 15 years the decline is 3.7% per year. Compared to 1990, the national population has halved. Based on Atlas data, the Dutch breeding population in 2013-15 was estimated at 3800-4800 pairs. Negative trends in nature reserves have been stronger than in agricultural areas since 1984 (Fig. 2). The trends per region / habitat show that Eurasian Curlews have virtually disappeared from mainland dunes in the western part of the Netherlands, in heathlands, peat moors and in peat bogs since 1984 (Fig. 3). The breeding numbers on the Wadden Sea islands are declining as well.
The distribution of the breeding population over the various habitats has changed radically in recent decades: from breeding mainly in nature reserves in the 1950s to mainly in agricultural areas nowadays (Fig. 5). In 2013-15, one third of the agricultural curlew-population bred on arable land and the remainder mainly on grassland. Breeding in arable habitat is of a more recent date (since circa 1980). Within nature reserves, grasslands with management for breeding birds are particularly important.
The average start of egg-laying is April 14th (1985-2018), and there is no significant advance or delay in this date (Fig. 9). Nesting success in farmland shows large annual fluctuations around an average value of 37.4%, with no clear trend in the period 2000-20 (Fig. 10). In 2009-14, nesting success of these, mostly protected, nests was above average, but decreased from 2015. The average nesting success in nature reserves is 63.4%.
We discuss a wide range of possible explanations for changes in trends and distribution, such as changes in natural habitats (due to changes in management, grazing and nitrogen deposition), low chick survival, and nest predation as main drivers. Data indicate a low and strongly decreased breeding success, both in heathland and agricultural land (Fig. 11 and 12). Insufficient reproduction is also considered to be the main reason for the decline in other parts of Europe, mainly due to intensification of agriculture in combination with increased predation pressure. Many Dutch habitats are now unsuitable and it is unlikely that sustainable populations could be restored in dune areas, heathlands, moors and bogs. Opportunities for improving breeding habitat lay in agricultural areas and on the Wadden Sea Islands.

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